This application claims the priority of German Patent Application Serial No. 199 01 496.5, filed Jan. 11, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to gripping devices for lifting loads, and in particular to an overhead clamp-type gripping device of a type including a carrier frame having attached thereon support elements which are movable relative to one another and carry confronting gripping elements for lateral engagement of a load.
U.S. Pat. No. 5,795,003, issued on Aug. 18, 1998, describes a gripping device of this type for grabbing loads from above. The gripping device is arranged on a hand-guided handling device and includes a carrier frame which can be lowered and lifted via the handling device in a vertical direction. The carrier frame has support elements for attachment of gripping elements which are aligned in substantial parallel relationship to the direction of the vertical axis and move in opposition to one another for lateral engagement of the load. The gripping elements have a configuration that is suited to the load being grabbed so as to grip the load from below in a form-fitting manner. To prevent the load being grabbed from pushing the gripping elements away from one another during transport, the gripping device is provided with a fastening mechanism to lock the gripping elements in place relative to one another.
This conventional gripping device suffers shortcomings as a result of the required grabbing of the load from underneath so that its use is unsuitable for many objects such as e.g. cardboard boxes and the like.
It is thus an object of the present invention to provide an improved gripping device, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved gripping device which is easy to handle and has a slender configuration while yet being able to reliably grab a load, without gripping the load from underneath.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a carrier frame movable in a vertical direction and having support elements positioned on both sides of the center plane and extending downwards from the carrier frame for movement relative to one another, with the support elements having longitudinal guides which define an upwardly open angle with respect to the center plane; a gripper unit which is received in the longitudinal guides of the support elements and includes gripping elements for laterally contacting a load, with the gripping elements being movable in load direction from a ready position in which the gripping elements are disposed at an upper end of the longitudinal guides and lockable in place by a locking mechanism, to an active position in which the gripping elements grab the load whereby during lifting of the carrier frame the gripping elements move relative to the support elements in the load direction to thereby automatically apply a clamping action with a clamping force which depends on the weight of the load, and by providing a fastening mechanism for permitting securement of a mutually fixed position between the support elements.
In accordance with the present invention, the clamping action of the gripping elements is dependent from the weight force of the load after the gripping elements firmly engage the load, whereby the engagement of the gripping elements is only of such extent as is necessary to accomplish a troublefree grabbing. Handling of the gripping device is easy when restraining the support elements in their movement by means of the fastening mechanism. The gripping device can be operated in a simple manner because the gripping elements can firmly engage a load between them, after the fastening mechanism is released. This can be done automatically, e.g. by utilizing the existing own weights of the load and the carrier frame.
The effectiveness of the gripping device according to the present invention is based on the principle that the weight of the load is utilized to act on the gripping elements so that the gripping elements can be pressed against the sidewalls of the load at a multiple of the weight.
According to another aspect of the present invention, the gripping elements swing about a pin which defines a horizontal pivot axis extending perpendicular to the longitudinal guides and parallel to the center plane, thereby accomplishing an even engagement of the gripping elements on the load. The clamping action can be further enhanced when providing pairs of longitudinal guides in opposite disposition.
In accordance with a simple embodiment of the gripping device, two longitudinal guides are provided which extend at an upwardly open spread angle relative to one another, with each of the two longitudinal guides supporting a gripping element whereby the two gripping elements have plate-shaped gripping areas in confronting disposition. Depending on the configuration of the carrier frame, the gripping areas of the gripping elements may face one another with or without lateral offset. The longitudinal guides are each formed as an elongate slot which is engaged by the pin of the pertaining gripping element. Suitably, both gripping elements define in their ready position an upwardly open spread angle and are held in this position by the locking mechanism, to ensure a smooth operation of the gripping device. A simple embodiment proposes the use of a spring force for holding the gripping elements in their ready position. An example may include spring-loaded locking members by which the gripping elements are cleared to pivot from their ready position only after a predetermined force is applied which overcomes the spring force exerted on the locking member.
According to another feature of the present invention, the load can be easily grabbed when the gripping device is so configured that the gripping elements are automatically forced into flat engagement with the sidewalls of the load before lifting the load, whereby the force is dependent on the weight of the carrier frame. Thus, the engagement and the load weight dependent clamping action are separated in time from one another. Engagement of the gripping elements can be realized in a simple manner by mounting the support elements to arms which are guided in the carrier frame for linear movement in horizontal direction in opposition to one another to thereby form a horizontal support.
According to another feature of the present invention, the support unit is realized by two angles having a horizontal arm forming the horizontal carrier and a vertical arm forming the support element. This configuration results in a stable and structurally simple configuration of the carrier frame.
Pickup and placement of the load as well as movement of the gripping elements in their ready position can be easily implemented when providing the gripping elements with horizontal brackets for engagement with the load when the carrier frame is positioned on the load.